But just before 1 p.m., the rally collapsed in the blink of an eye. Plug Power closed down 41%.

One reason for the sell-off could be a report issued by Citron Research, an influential online stock commentary website.

In an unsigned note, the firm called PLUG a "casino stock" and suggested it would return to its one-time trading price of $0.50. They write:

A casino stock... is the lowest form of speculative moonshot. A casino stock can trade twice its outstanding shares in a single day, while turning over its entire float on people gambling that they can find a buyer at a higher price … Who really cares about anything else, right? The recent volume and share price surge in Plug Power (NASDAQ:PLUG) demonstrates how Wall Street treats this stock: nothing more than a casino.

Among the problems Citron says its found:

The company has consistently fallen short of its own quarterly forecasts.

There's an apparent lack of conviction among Plug's own management, who at one point refused to buy in on a capital round of just $0.15 a share.